Hello, I'm new to the brickboard and am most humbly requesting help. All the research here and at various other sites is getting me close, but nothing seems to have targeted my specific issue:

Car is a 1990 740, 5 speed (M47? No overdrive). Regina ignition. Car ran fine when I bought it about 2 months ago. Gradually became more difficult to start. Finally refused to start at all. Turns over fine, just won't start. Replaced battery for good measure. Went thru troubleshooting (Fuel pressure regulator, Fuel Pump, Fuel Pump Relay, Replaced all ignition wires/plugs, distributor cap, rotor, IAC works, cleaned throttle body, new gasket, inspected vaccum hoses as best I could, base idle reset and TPS is set correctly).

Here's the odd bit: Almost 100% of the time when it does this, I can get it started by jump starting from my S90.

Seems to happen most often if the car hasn't been driven in a few days.

Once it does start (normally, when it will, or from the jump start) it runs horribly for about 3 minutes (requires a foot on the gas to keep it running, stalls when RPM drops after "blipping" the throttle). Once warm it idles well at 750 with a very slight misfire. Misfire increases at 1500 RPM, no load (car in neutral). No misfire noted while accelerating, under load in gear. So far no warm restart issues.

I've had a couple of codes pop up (Air Temp Sensor, and O2 sensor) both with check engine light illuminated. Codes will clear and CE light will reset. The codes have only popped up after the engine stalls during the intial warm-up.